What does this technology aim to do?
- Reduce carbon dioxide emissions
- Effectively use surplus renewable energy
This system is significant as a fuel producing system which doesn’t add to carbon dioxide emissions to the atmosphere
Fig.1 Methanation system
Methanation is a method which converts a mixture of carbon dioxide and hydrogen to methane. Methanation system employs a hydrogen generator, CO2 capture, methanation reactor and utilization equipment of CH4.
It is a greenhouse gas reduction system that obtains electrode for electrolysis from renewable energy. In addition, by using surplus renewable energy, it will be able to equalize the demand gap.
What is biomethanation ?
It is methanation using methanogenesis.
We can get methane in mild condition;
37 degrees and at atmospheric pressure.
Fig.2 Biomethanation
In this study, Biogas from anaerobic digestion in wastewater treatment plant is targeted.
Fig.3 Biomethanation system in wastewater treatment plant
Advantages
- Biogas doesn’t contain oxygen, so it can be used without CO2 separation process.
- Methanogenes, in seed sludge, can be supplied from anaerobic digestion reactor.
Subject of improvement
Goal: Miniaturization of reactor
Biomethanation reactor is about 100 times bigger in size than that in catalytic method
Problem: Hydrogen solubilization
Biomethanation has an advantage in reaction condition which is mild temperature 37degree. But its reactor size is over 100 times bigger than that in the catalytic method. To miniaturize the reactor, effective solubilization of hydrogen is important. Crude gases of biomethanation are carbon dioxide and hydrogen. The former is easily soluble in water, but the latter has 1/40 of its solubility. To accelerate bioconversion, hydrogen dissolution should be more effective.
Subject of improvement
Solution：Application of microbubble generator
Fig.5 Example for Biomethanation reactor employed microbubble generator
Surface area increases approximately 1000 times → Improved hydrogen diffusion
→ Achievement of reactor miniaturization
To dissolve hydrogen effectively, diffuser selection is important. We propose a reactor implementing a microbubble generator, which produces smaller bubbles approximately 2 μm. These are 1000 times smaller than those produced by a conventional diffuser. It improves the diffusion of hydrogen so accelerating reaction efficiency and reaction time.